Further, according to Lemma 2 from [1]} the function \(t\longrightarrow x_{t}\)  is derivable almost everywhere and one has
\(\left\Vert \frac{d}{dt}x_{t}\right\Vert \le \frac{p}{t}\Vert x_{t}\Vert \mbox{ for almost every} t\ge t_0.\) 
